Thermoplastic compositions having improved stress cracking properties



United States Patent 3,162,698 THERMQPLASTIQ t'JQMhOfi-ETEGNS HAVTNG PROJVED STRES CRACKBNQ PRillllERTliES Bernard it). Baum, Piainiield, Nail, aasignor to Union Carbide Corporation, a corporation at New York No Drawing. Filed June 19, 1962, tier. No. 293,472 9 Claims. (Cl. zse sar The invention relates to mixtures of olefin high polymers and ethylene/bicycloheptene and/ or ethylene/bicycloheptadiene copolymers. In a particular aspect, the invention relates to mixtures of olefin high polymers and ethylene/bicycloheptene and/or ethylene/bicycloheptadiene copolymers which exhibit superior stress crack resistance compared with olefin high polymers alone.

Olefin high polymers, especially olefin high homopolymers and copolymers derived from monoolefinically unsaturated monomers, monoolefins, have such poor stress crack resistance that they are rendered virtually useless for a great number of applications for which they otherwise would be well suited because of the proximity of a chemically active material.

It has now been discovered that surprising and marked improvement in the stress crack resistance of olefin high polymers can be obtained by the mixing therewith to substantial homogeneity, i.e., to the formation of an intimate admixture, certain amounts of an ethylene/bicyoloheptene copolymer or an ethylene/bicycloheptadiene polymer or a mixture thereof. These compositions are useful for making bottles and other containers and molded articles as well as films and coatings, and are particu larly advantageous where high stress crack resistance is a desirable or essential feature of the article.

The term high polymers is used in the present specification and claims to denote homopolymers of monoolefins containing preferably from 2 to 10 carbon atoms inclusive, copolymers of two or more monoolefins containing from 2 to 10 carbon atoms inclusive and copolymers containing about 80 percent by weight, and preferably at least 90 percent by weight, of one such monoolefin with up to about percent by weight and preferably up to about 10 percent by Weight, of at least one other olefiflically unsaturated monomer coplymerizable therewith, such as, for example, vinyl esters, vinyl ethers, acrylic acid and methacrylic acid and esters thereof such as ethyl acrylate, methyl methacrylate, and the like, in every case the olefin high polymer being of sufficient molecular weight that it is considered a high polymer rather than a wax, i.e., it has a molecular Weight of at least about 10,606, conveniently determined by a melt index of less than about 1,600, and preferably less than about 100. Illustrative of the suitable homopolymers and copolymers which can be used as olefin high polymers to be modified by addition thereto of an ethylene/ bicycloheptene and/or ethylene/bicycloheptadiene copolymer are the normally solid polyethylenes having a density of from about 0.91 to about 0.97 as well as other olefin homopolymers such as polypropylene, p'olybutenel, poly(3-methylpentenel), polyhexene-l, polyoctene-l, polydecene-l, and the like, and olefin copolymers, as for example ethylene/propylene copolymers, ethylene/butene-l copolymers, ethylene/ethyl acrylate copolymers, ethylene/methyl methacrylate copolyrners, ethylene/vinyl acetate copolymers, and the like. This list, however, is intended to be merely illustrative and should not be considered as restrictive of the olefin high polymers which can be used in the compositions of this invention.

The above-described olefin high polymers constitute from about 70 percent by weight to about 99 percent by weight of the olefin high polymer-ethylene/bicycloheptene and/ or ethylene/bicycloheptadiene copolymer mixtures of this invention. The referred amount of 3,ib2,fi% Patented Dec. 22, 1964 olefin high polymer in the mixture is from about percent by Weight to about percent by weight.

The olefin high polymer-ethylene/bicyc1oheptene and/- or ethylene/bicycloheptadiene copolymer thus comprises from about 1 percent by weight to about 39 percent by weight ethylene/bicycloheptene or ethylene/bicycloheptadiene copolynier, with an amount of either or a total of these copolymers of from about 10 percent by weight to about 20 percent by weightbeing preferred.

The ethylene/bicycloheptene or ethylene/bicycloheptadiene copolymers useful as additives to olefin high polymers in this invention contain from about 1 percent by weight to about 30 percent by weight combined bicycloheptene or bicycloheptadiene, and preferably from about 2.5 percent by weight to about 15 percent by weight combined bicycloheptene or bicycloheptadiene and therefore from about 70 percent by weight to about 99 percent by weight, and preferably from about 85 to about 97.5 percent by weight, combined ethylene.

Bicycloheptene and bicycloheptadiene monomers which can be copolymerized with ethylene for use in the invention are bicycloheptenes having the structural formula and bicycloheptadienes having the structural formula wherein R and R are members selected from the group consisting of hydrogen or lower alkyl radicals, e.g., those having from 1 to 4 carbon atoms inclusive, and R R R and R are members selected from the group consisting of hydrogen, lower alkyl radicals, e.g., those having from 1 to 4 carbon atoms inclusive, or aryl radicals. The preferred bicycloheptene comonomer is bicyclo [2.2.1.]hept-2-ene, and the preferred bicyclolieptadiene comonomer is bicyclo [2.2.1]hepta-2, diene.

The ethylene/bicycloheptene and ethylene/bicycloheptadiene copolymers used in this invention are normally solid copolymers having a melt index of less than about 1,000, and preferably less than about 100. Suitable copolymers are prepared by copolymerizing ethyene, bicycloheptene and/ or bicycloheptadiene by a free radical process using bulk, solution, emulsion or suspension techniques at pressures about 500 atmospheres, and above and preferably from about 750 to 3,000 atmospheres, at a temperature of from about 40 C. to about 350 C. and preferably from about C. to about 225 C. to obtain a copolymer having the structure given in Examples 17 and 18 hereof. Alternatively suitable copolymers can be obtained by a coordination catalyst such as the product of titanium tetrachloride and lithium aluminum tetraalkyl. These polymers which have the wherein n and m are integers such that the copolymer is normally solid, are described and claimed in US. Patent No. 2,799,668 to A. W. Anderson et al., issued July 16, 1957, which is herewith incorporated by reference.

The method in which the olefin high polymerethylene/bicycloheptene and/or ethylene/bicycloheptadiene copolymer blend is prepared is not narrowly critical.

Any conventional method which provides a homogeneous mixture can be employed. One method which has been found to be satisfactory is to flux mixtures of polymers and any desired additives in a Banbury mixer for a three copolymers are substituted for low density polyethylene. Similar stress crack improvements are obtained.

EXAMPLE 16 to five cycle and then w the material on 5 Example 1 is duplicated except that an equal weight i d P before transfemng It mto the rolls of a mixture of ethylene/bicyclo[2.2.1]hept-2-ene copolymer i? 5; 5 f bl t th and ethylene/bicyclo[2.2.1]hepta-2,5-diene copolymer is th en er a g i substituted for ethylene/bicyclo[2.2.1]hept-2-ene copoly- {011a P as mcu "g u mer. Similar stress crack improvement is obtained.

not limited to, modifiers, opacifiers, fillers, lubricants, 10

stabilizers, colorants, and the like can be added to the EXAMPLE 17 compositions of the invention, if desired.

The practice of the present invention is illustrated Into a siamless Steel-lined stmed autoclave of p by the following examples wherein all parts and percenti csapamy g l fl fg a es areb wei ht unl sotherwises ecified. a Percent y Welg t so uuon o Peron e g y g as p in benzene, and 19.6 grams of 5-methylb1cyclo-['2.2.1]-

EXAMPLES hept-Z-ene. The autoclave was sealed, flushed with An olefin high polymer was fluxed on a two-roll mill ethylena, pressoured w Ethylene 21000 P and at 110 C. and the ethylene/bicycloheptene or ethylene/ mated to 160 wlth Ylgorous agltatlonethyl bicycloheptadiene copolymer milled in immediately after 20 ene P F was afllusted to 1 m? and the fiuxing The time of working was about five minutes polymerization was earned out maintaining the pressure including ten end passes to disperse to homogeneity the and tempelmwre at about the Stated values W hourcopolymer additive Control Samples were prepared in After cooling, the autoclave was vented, the solid ethylthe same manner except that no copolymer was added. Y F copolymer was To determine stress crack resistance, a 125 mil comtered: wahed wlth methanol: and dnedcopolymer pression molded specimen 0.5" x 1.5" was slit along the was a w granular resmlong dimension The slit was 20 mils deep and 75 mils The infrared spectrum was consistent with an ethylene/ long. The speicmen was then bent 180. Ten such bent s'methylblcyclolz-z'nhgpt'zelm copolymer having the specimens were held in a channel which was then im- Structural formula mersed in Hostapal (a non-ionic surfactant believed to be similar to nonyl phenoxy polyoxyethylene ethanol) at E CH 50 C. in a test tube. Two such channel devices were 2 n put into each tube, providing twenty specimens per test.

Time to failure of any one specimen was the appearance of a crack perpendicular to the slit; P is the time to CH failure of 50 percent ('i.e., 10) of the specimens. 3 m

Melt index was measured at 190 C. and 44 psi. in accordance with ASTM D-1238-57T. EXAMPLE 18 Density was determined in acocrdance with ASTM The procedure of Example 17 was followed except that D 1505 5'7T for S-methylbicyclo[2.2.1]hept-2-ene was substituted bi- Results of tests conducted on the olefin high polymercyclo[2.2.1]hepta-2,5-diene. ethylene/bicycloheptene and ethylene/bicycloheptadiene The infrared structure of the product was consistent copolymer mixtures of the invention (Examples 1-13) with an ethylene/bicycle[2.2.1]hepta-2,5-diene co 01 met P y are summarized in Table I. having the structural formula TABLE I Olefin High Polymer Copolymer Example N mber Melt Density Co- Oopolyrner Percent Stress Index Copolymer momomer, Melt Index Copolymer Cracking,

Percent In Blend HourstoFw Control 1 Low density polyethylene... 2.0 0.92 n 0 0 2 1 do 2.0 0.92 Egh r z lgnelBlcyclofifl.llHept- 1 3.2 20 1 2.0 0.92 do.'. 2.5 0.1 2.0 0.92 do. 5 1.7 38 3. .3; go is 7.8 20 500 110 01045 'fiiici g 8 1.0 0.045 Eglgggne/Bieyclollll]I-Iept- 2.5 0.1 20 500 0.0 0.96 None: 0 o 1 0.6 0.96 glgne/BicyelMZZHHept- 2.5 0.1 20 50 2.0 0.92 None 0 0 2 2.0 0.92 Et21ylene/Bicycl0[2.2.11Hept- 2.5 0.1 1 60 8% at 233 210 0192 rgr g gggginane: 5' 2:4 20 2588 2.0 0.92 Ethsylfiliigllllgieyeldl.1]Heptu 5 1.0 20 500 EXAMPLE 14 Example 1 is duplicated except that polypropylenes are substituted for low density polyethylene. Similar stress crack improvements are obtained.

EXAMPLE 15 Example 1 is duplicated except that ethylene/propylene The letters m, n and x in the above formulas are in-.

tegers such that the polymers are normally solid and the polymers comprise from 70 to 99 percent combined ethylene by weight.

The polymers employed in the preceding examples were prepared in the manner of Examples 17 and 18.

EXAMPLE 19 Example 1 is duplicated substituting a copolymer prepared by the method of US. Patent No. 2,799,668 above mentioned. Improved stress cracking properties are obtained.

What is claimed is:

1. A composition exhibiting improved stress crack resistance wherein from about 70 percent by weight to about 99 percent by Weight of a high polymer of a monoolefin containing from two to ten carbon atoms inclusive having a melt index of less than about 1,000 decigrams per minute measured in accordance with ASTM 1238-57T at a temperature of about 190 C. and a pressure of about 44 pounds per square inch is in intimate admixture with from about 1 percent by weight to about 30 percent by weight of a copolymer of ethylene with a comonomer selected from the group consisting of (A) a bieycloheptene monomer having the structural formula wherein R and R are members selected from the group consisting of hydrogen and lower alkyl groups having from 1 to 4 carbon atoms inclusive and R and R are members selected from the group con-' wherein R and R 6 are members selected from the group consisting of hydrogen, lower alkyl radicals having from 1 to 4 carbon atoms inclusive, and aryl radicals; and

(C) mixtures of (A) and (B), said ethylene/bicycloheptene and ethylene/bicycloheptadiene copolymers having a melt index of less than about 1,000 decigrams per minute measured in accordance with ASTM 1238-57T at a temperature of about 190 C. and a pressure of about 44 pounds per srguare inch and comprising from about 70 percent by weight to about 99 percent by weight combined ethylene and from about 1 percent by weight to about 30 percent by weight of the combined comonomer.

2. The composition claimed in claim 1 wherein said olefin high polymer is polyethylene having a density of from about 0.91 to about 0.97.

3. The composition claimed in claim 2 wherein said ethylene/bicycloheptene copolymer is an ethylene/bicyc1o-[2.2.1]hept-2-ene cop olymer.

4. The composition claimed in claim 2 wherein said ethylene/bicycloheptene copolymer is an ethylene/bicyclo- [2.2. 1 hept-2-ene-5-methylene copolymer.

5. The composition claimed in claim 2 wherein said ethylene/bicycloheptadiene copolymer is an ethylene/bicyclo [2.2.l]hepta-2,5-diene copolymer.

6. A composition exhibiting improved stress crack resistance wherein from about percent by weight to about percent by weight of a polyethylene having a melt index of less than about decigrams per minute measured in accordance with ASTM l238-57T at a temperature of about C. and a pressure of about 44 pounds per square inch and a density of from about 0.91 to about 0.97 is in intimate admixture with from about 10 percent by weight to about 20 percent by weight of a copolymer of ethylene with a comonomer selected from the group consisting of (A) a bicycloheptene monomer having the structural formula (B) a bicycloheptadiene monomer having the structural formula wherein R and R are members selected from the group consisting of hydrogen, lower alkyl radicals having from 1 to 4 carbon atoms inclusive and aryl radicals and (C) mixtures of (A) and (B), said ethylene/bicycleheptene and ethylene/bicycloheptadiene copolymers having a melt index of less than about 100 decigrams per minute measured in accordance with ASTM 1238-57T at a temperature of about 190 C. and a pressure of about 44 pounds per square inch and comprising from about 85 percent by weight to about 97.5 percent by weight combined ethylene and from about 2.5 percent by weight to about 15 percent by weight of the combined comonomer.

7. The composition claimed in claim 6 wherein said ethylene/bicycloheptene copolymer is an ethylene/bicyclo- [2.2.1]hept-2-ene copolymer.

8. The composition claimed in claim 6 wherein said ethylene/bicycloheptene copolymer is an ethylene/bicycle- [2.2.1]hept-2-ene-5-methylene copolymer.

9. The composition claimed in claim 6 wherein said ethylene/bicycloheptadiene copolymer is an ethylene/bicyclo [2.2. l hepta-2,5 -diene cop olymer.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A COMPOSITION EXHIBITING IMPROVED STRESS CRACK RESISTANCE WHEREIN FROM ABOUT 70 PERCENT BY WEIGHT TO ABOUT 99 PERCENT BY WEIGHT OF A HIGH POLYMER OF A MONOOLEFIN CONTAINING FROM TWO TO TEN CARBON ATOMS INCLUSIVE HAVING A MELT INDEX OF LESS THAN ABOUT 1,000 DECIGRAMS PER MINUTE MEASURED IN ACCORDANCE WITH ASTM 1238-57T AT A TEMPERATURE OF ABOUT 190*C. AND A PRESSURE OF ABOUT 44 POUNDS PER SQUARE INCH IS IN INTIMATE ADMIXTURE WITH FROM ABOUT 1 PERCENT BY WEIGHT TO ABOUT 30 PERCENT BY WEIGHT OF A COPOLYMER OF ETHYLENE WITH A COMONOMER SELECTED FROM THE GROUP CONSISTING OF (A) A BICYCLOHEPTENE MONOMER HAVING THE STRUCTURAL FORMULA 